Estimation of Local Anisotropy Using Polarisations and Travel Times From the Oseberg 3DVSP
Paul Williamson, Eric Maocec, 2001. "Estimation of Local Anisotropy Using Polarisations and Travel Times From the Oseberg 3DVSP", Anisotropy 2000: Fractures, Converted Waves, and Case Studies, L. Ikelle, A. Gangi
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Observations of polarisations and slownesses at downhole receivers in walkaway or multioffset VSP experiments can in principle be inverted to give the anisotropic seismic velocity of the earth in the vicinity of the receiver array. In practice, such inversions have been only rarely reported, possibly due to a general lack of confidence in polarisation measurements. We apply such an inversion to the direct P-wave arrivals from a 3D VSP dataset acquired at the Oseberg field in the Norwegian North Sea. The large size of this dataset ensures that the result is more stable than those from comparable inversions applied to standard 2D datasets. Comparison with the result from the more established, but more restricted, method of inversion of surface and receiver slownesses showed a large discrepancy. Further investigation revealed that this is due to acquisition-related coherent noise on the estimated surface slownesses; there is no corresponding effect on the polarisation inversion because each shot is treated independently. We therefore prefer the result from the polarisation inversion in this case.
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“This volume contains 25 papers that represent most of the best work in seismic anisotropy in 1998 and 1999. Fracture characterizations and processing of converted waves are the two main topics covered in this volume. They are addressed from both theoretical and practical viewpoints. Also included are papers describing the historical roots of seismic anisotropy.”